Gas seal

Abstract

A gas seal arrangement for use in a blown-fiber duct (11) which extends outside a building from within a building, the gas seal arrangement being inserted in a segment of said duct to prevent the flow of gas into the building via said duct (11) and being unidirectionally flexible, the arrangement comprising a connector (15) sealingly connected to respective blown-fiber duct portions on each side thereof, along which the transmission fiber (P) is disposed, the connector further comprising a flange portion (12a) and a flexible body portion (12b), the flexible body portion being arranged to collapse inwardly around a transmission fiber (P) when the transmission fiber has been installed through said duct segment , the flexible body portion being arranged to open to permit gas flow outwardly from the building through said duct segment when the gas flow pressure exceeds a predetermined level, i.e. during the time when the fiber is blown into the duct, and wherein the flexible body portion extends along said duct segment when at rest and is arranged to form an elongate seal with the surface of an installed transmission fiber (P) resistant to opening to gas flowing inwardly. <MATH>

I claim: 
     
       1. A sealing arrangement for a passageway carrying a transmission line package, the arrangement comprising a coupling portion for connection to respective passageway portions on each side thereof, a flexible seal located in the coupling portion and comprising a flexible body portion, the flexible body portion being arranged to collapse inwardly to seal around a transmission line package when the transmission line package is installed through the coupling portion, and the flexible body portion being arranged to open to permit fluid flow through the coupling portion when the fluid flow pressure exceeds a predetermined level, wherein the coupling portion is provided with at least one vent disposed so that pressure externally of the coupling portion tends to cause inward deformation of the body portion of the seal to increase its resistance to opening. 
     
     
       2. A sealing arrangement as claimed in claim 1, wherein the flexible seal comprises a tubular member having a waisted intermediate portion that forms the seal, and wherein the ends of the tubular member are secured to the inner wall of the coupling portion with the or each vent disposed between the locations at which the ends of the tubular member are secured. 
     
     
       3. A sealing arrangement as claimed in claim 1, wherein the flexible seal has substantially flat opposing surfaces. 
     
     
       4. A sealing arrangement as claimed in claim 1, wherein the seal opens unidirectionally. 
     
     
       5. A blown-fibre installation comprising at least one blown-fibre duct which extends outside a building from within the building, a gas seal being provided in a segment of said duct to prevent the flow of gas into the building via said duct, characterised in that said gas seal is flexible and comprises a flexible body portion, the flexible body portion being arranged to collapse inwardly around a transmission line package when the transmission line has been installed through said duct segment, the flexible body portion being arranged to open to permit fluid flow through said duct segment when the fluid flow pressure exceeds a predetermined level, and wherein the flexible body portion extends along said duct segment and is arranged to form an elongate seal with the surface of an installed transmission line package. 
     
     
       6. A blown-fibre installation as claimed in claim 5, wherein a transmission line package extends through said seal. 
     
     
       7. An installation as claimed in claim 6 wherein said flexible body portion sealingly conforms to the surface of said transmission line package.